This invention relates to the management of the memory space of a storage device in a computer system, and particularly to a method of seeking vacant (free) memory areas for the allocation of files of various sizes in a large-capacity disk memory.
A conventional technique for the management of memory space of the main memory which is a storage device is described in JP-A-Hei3-92941. Another conventional technique for the assignment of memory space on a magnetic disk (DASD) which is one of storage devices is described in JP-A-Sho59-173865.
According to this last mentioned prior art, the memory space of the storage device is partitioned into unit blocks of a single size, with each block being represented by one-bit data on a bit map so that the bit value reflects the vacant or occupied state of each unit block, and the management of memory space is implemented for each block based on its bit value on the bit map.
The above-mentioned JP-A-Sho59-173865 describes the overhead problem associated with counting the number of consecutive bits in seeking a continuous free area based on the bit map, and it offers a method of byte-wise (8 bits) seek using two kinds of conversion tables for the bit map to thereby dissolve the overhead problem. However, this method merely improves the seek efficiency by eight fold at most, and the efficiency will decrease as the DASD capacity continues to increase.
The prior art of the above-mentioned JP-A-Hei3-92941 uses several bit maps for dealing with unit memory areas of different sizes, and seeks a single free unit memory area of one of the sizes demanded by selectively using a bit map for a unit area size equal to the required size. In this case, it is presumed that the required area size must be equal to one of the different sizes. This prior art cannot be applied when the demanded size is different from any of the provided sizes.